Existing methods for multicast delivery—i.e. the delivery where transmission of a single protocol data unit (PDU) reaches a group of one or more destinations—over radio interfaces use broadcasting on the radio link to reach unidirectionally all recipients covered by the cell, e.g. to reach all mobile stations which are located in the area of one base station. The delivery of a communication message may be for example a weather forecast, a traffic announcement or an advertisement.
Broadcasting to the whole cell area uses a lot of power, which in turn causes a lot of cross-channel interference. Also, a robust channel coding is usually required to reach the full coverage area of the cell, especially because there is usually no feedback possibility for the receivers to indicate lost radio frames.
On the other hand, in situations where there is only one, or a few recipients on the cell area, it would be cheaper and more resource-efficient to send the information to the recipients individually using dedicated channels. Unicasting transmission may be described as a transmission of a single protocol data unit PDU to a single destination.
However, other radio systems carry all user plane data traffic on dedicated channels. Such systems waste radio resources, if the same information is being sent separately to many users on the cell area. Also, when the number of group members on the cell area is larger than the number of available dedicated channels, all users cannot be served.
One of the disadvantages associated with the above-mentioned arrangements is thus that shared channel based systems waste radio spectrum, if the number of group members is low on the cell area while dedicated channel based systems waste radio spectrum, if the number of group members is high on the cell area.